THE  PREPARATION  OF  METALLIC 
LANTHANUM 


BY 


ROGER  GREENLEAF  STEVENS 

B.S.  University  of  Illinois,  1920 


THESIS 

SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 
FOR  THE  DEGREE  OF  MASTER  OF  SCIENCE  IN  CHEMISTRY 
IN  THE  GRADUATE  SCHOOL  OF  THE  UNIVERSITY 
OF  ILLINOIS,  1922 


URBANA,  ILLINOIS 


\c5  6*  6- 


UNIVERSITY  OF  ILLINOIS 


THE  GRADUATE  SCHOOL 


May_  2.5. 


—1922— 


I HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 


SUPERVISION  BY_  . Roger-  Qreenle-af  S t e vens 


ENTITLED__Ilie— Preparation  of -Me  ta  11  ic-  Lanthannm- 


BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR 


THE  DEGREE  OF 


¥ aatflu  of  ? o.  I PnRfi- 


In  Charge  of  Thesis 


Head  of  Department 


Recommendation  concurred  in’* 


Committee 


on 


Final  Examination* 


^Required  for  doctor’s  degree  but  not  for  master  s 


A OQ/M  Q 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/preparationofmetOOstev 


TABLE  OF  CONTENT? 


I.  ACKNOWLEDGMENT  Page  No. 

II.  INTRODUCTION  1 

Object  1 


Occurrence  1 

Historical  1 


III.  THEORETICAL  

IV.  EXPERIMENTAL  

Source  of  material  

Preparation  of  anhydrous  LaCl^  

Factors  in  electrolysis  

Discussion  of  difficulties  encountered  and 
suggested  remedies 

Result  of  run 3 

V.  CONCLUSION 


3 


3 

3 

5 

10 


15 

18 

24 


Summary 34 

Bibliography  35 


ACKNOWLEDGEMENT 

Til 3 writer  desires  to  express  his  appre- 
ciation to  Dr.  H.  0.  Kreraers  for  the  U3e  of  apparatus 
and  for  many  helpful  suggestions.  Appreciation  is  also 
due  Dr.  3.  S.  Hopkins  for  valuable  suggestions  and  in- 
terest shown  throughout  the  work. 


INTRODUCTION 

The  object  of  the  present  work  was  to  prepare  metallic 
lanthanum  in  such  amounts  and  form  aG  to  be  able  to  study  the 
physical  and  chemical  properties  in  a later  investigation. 

Lanthanum  is  one  of  the  elements  included  in  the 
cerium  group  of  rare  earths  and  is  found  in  a large  number  of 
widely  distributed  minerals  which  include  orthite,  cerite,  lan- 
thanite,  monazite,  fluocerite,  yttrocerite,  bastn&site,  tysonite, 
parisite  and  melanocerite^.  Of  these,  mcnazite  is  by  far  the 
most  important  and  because  of  the  thorium  content  finds  wide  use 
in  the  gas  mantle  industry.  Consequently,  the  residues  from  this 
industry  form  a prolific  source  for  the  rare  earths. 

3 

Lanthanum  wa3  discovered  in  18  33  by  Mosander  . After 
the  discovery  of  lanthanum,  attention  of  investigators  was  direct- 
ed to  obtaining  pure  lanthanum  . As  a result  it  was  found  that 
lanthanum  compounds  are  most  easily  obtained  by: 

1.  The  fractional  crystallization  of  the  double  magnesium 

3 

nitrates  of  the  cerium  earths  after  the  cerium  has  been  removed  . 

3.  The  double  carbonate  method  after  the  separation  of 
4 

cerium  . 

The  first  method  has  been  used  in  thi3  laboratory  with 
good  results. 

Most  of  the  previous  work  on  the  rare  earth  metals  has 
been  concerned  with  the  preparation  of  misch  metal,  (a  mixture  of 
the  metals  of  the  cerium  group  rare  earths)  and  the  preparation 
of  metallic  cerium  . However,  Muthmann  and  his  associates,  in 


- 


• • 'i " 


, 


' 


- 3 - 

1803,  began  an.  investigation  of  the  preparation  of  the  individual 

metals  of  the  cerium  group  and  obtained  lanthanum  in  an  impure  and 

finely  divided  state  which  necessitated  subsequent  fusion  under 

3 

B aCl 3 for  pur  i f i c at  ion  , 

THEORETICAL 

In  the  preparation  of  metals,  two  general  methods  are 

used: 

(1)  Reduction  of  the  oxides  or  chlorides  by  one  of  the  very 
electropositive  metals. 

(2)  Electrolysis  of  a fused  salt  or  an  aqueous  solution  of  the 

salt . 

The  first  method  was  discarded  because  of  the  very 

strong  electropositive  nature  of  metallic  lanthanum  itself  and  also 

because  of  the  unsuccessful  attempt  of  Alcan  Hirsch  to  even  obtain 

metallic  cerium  (which  is  less  electropositive  than  lanthanum)  by 
7 

this  method  . 


Consequently,  attention  was  directed  to  the  second 
method.  The  use  of  aqueous  solutions  was  out  of  the  .question  be- 
cause of  the  reason  stated  above  and  thus  the  problem  resolved  it- 
self into  the  study  of  the  electrolysis  of  a fused  salt.  It  wa3 
necessary  to  prepare  some  anhydrous  salt  of  lanthanum  and  because 
the  electrolysis  of  the  fused  chlorides  is  a more  general  procedure, 
study  was  made  of  the  preparation  and  electrolysis  of  fused  lan- 
thanum chloride. 


. 


■ . 


. 


' 
. 


. 


- 3 - 

SOURCE  OF  MATERIAL. 

The  double  magnesium  nitrates  of  lanthanum  were  used 

as  the  source  of  material.  The  nitrates  were  prepared  and  frac- 

tionated  by  Dr.  L.  F.  Yntema  and  showed  no  traces  of  the  two  most 

likely  impurities  to  be  present,  praseodymium  and  neodymium,  when 

the  absorption  spectrum  was  examined. 

In  order  to  replace  the  above  material,  fractionation 

of  the  double  magnesium  nitrates  of  lanthanum,  praseodymium  and 

3 

neodymium,  was  undertaken".  This  material  had  already  been  frac- 
tionated by  other  workers  in  this  laboratory  until  it  was  rich  in 
lanthanum,  praseodymium  end  neodymium.  After  30  crystallizations 
the  following  results  were  noted: 


Fr action 

Nd. 

Pr. 

1 

none 

none 

3 

t! 

trace 

3 

Less  than  .01%  NdgOj 

More  than  0.1%  PrgOs 

4 Hd  #2  line  faint 

Fractions  which  were  shown  to  be  free  from  praseodymium 
and  neodymium  according  to  the  absorption  spectra  were  set  out  from 
time  to  time.  After  70  fractionations  about  one-half  of  the  ori- 
ginal showed  no  absorption  spectrum.,  thus  indicating  the  absence 

of  praseodymium  and  neodymium. 

In  connection  with  the  separation  of  lanthanum  from 

praseodymium  and  neodymium,  it  might  be  mentioned  that  the  method 
of  Prandtl  and  Rauchenberger  was  tried  using  a small  amount  of 


I 


4 


material  . The  theory  is  "based  on  the  following  reversible  re- 
action: 


III 


MeCl3  “f  3NH3  + 3HS°  — 


III 

Me (OH) 


3NH4C1. 


They  give  experimental  data  on  the  solubilities  of  lanthanum, 
praseodymium,  neodymium  and  samarium  chlorides,  nitrates,  double 
magnesium  nitrates,  and  double  zinc  nitrates  in  solutions  contain- 
ing varying  amounts  of  NH^Cl  in  the  case  of  the  chlorides  and 
NE4N03  in  the  case  of  the  nitrates.  Because  the  material  was  al- 
ready in  the  form  of  double  magnesium  nitrates,  the  purification 
of  lanthanum  was  undertaken  according  to  the  following  equation: 

III  III 

2Me (W03)  3Mg(N03)  g-j-SNHg-j-SHgO  ~ — * 2Me(0H)3  3Mg(H03)2 

6NH4T?03. 


It  is  claimed  that  the  most  rapid  separation  occurs  in  a 5-normal 
HH4H03  solution  at  50°0.  At  this  concent  ration  and  temperature, 
the  following  solubilities  in  100  grams  of  solution  are  given: 


L 3 

^r3C3 

Nd203  

Thus,  upon  continued  fractionation,  the  lanthanum  would  tend  to 

concentrate  in  the  soluble  end  and  the  praseodymium  and  neodymium 

in  the  insoluble  end,  A sufficient  amount  of  material  containing 
lanthanum  and  praseodymium  ’was  taken  so  that  all  the  praseodymium 

which  was  present  would  be  theoretically  precipitated  according 

to  the  above  figures, 

Eighty  grains  of  crystals  of  the  double  magnesium 
nitrates  were  weighed  out  and  dissolved  in  2 liters  of  a 5 U 


- 5 - 


NH4NO3  solution.  Twenty-six  cc.  of  NHqOH  (sp.  gr.  .90)  were  added 
for  each  precipitation.  This  amount  was  calculated  from  the  above 
equation.  The  lanthanum  double  magnesium  nitrate  tended  to  remain 
in  solution  while  the  praseodymium  double  magnesium  nitrate  was 
precipitated  as  the  hydroxide.  The  precipitates  were  dissolved 
in  HC1  and  the  colors  noted. 

Fraction  Color 

1 Green 


3 « 

4 Faintly  green. 

5 Very  " " 

The  material  left  in  solution  was  precipitated  as  the  oxalate, 
ignited  and  dissolved  in  HC1.  No  green  color  was  visible  and  the 
absorption  spectrum  showed  the  absence  of  praseodymium. 

THF  PREPARATION  OF  ANHYDROUS  LaCl3 


There  have  been  a good  many  methods  proposed  for  the 
preparation  of  the  anhydrous  chlorides  of  the  cerium  group  of  rare 
earths.  Hirsch  has  tried  out  a number  of  the  methods  and  found 

7 

only  one  of  these  successful'.  Consequently,  this  method,  namely, 
the  heating  of  the  hydrated  chlorides  in  dry  HC1  gas,  wa3  studied 
with  the  point  in  view  of  making  improvements  in  the  apparatus  or 
devising  an  entirely  different  form  of  dehydrating  apparatus. 

Since  the  chloride  crystallizes  with  3-?  molecules  of 
water^~,  it  was  found  necessary  to  heat  very  cautiously  until  the 
monohydrate  was  formed  and  then  the  final  heating  could  be  carried 


. 

. 


* 


. 


. 


. 


. 


. 


' 

. 

..  | '•  | 


- 6 - 

out  at  a higher  temperature  and  without  much  care.  If  the  initial 

heating  were  carried  out  at  tec  high  a.  temperature,  the  basic 

chloride  was  easily  formed  and  the  material  would  not  fuse  to  a 

clear  melt.  Hermann  states  that  hydrated  lanthanum  chloride  loses 

both  HgO  and  HC1  when  strongly  heated  and  forms  the  basic  chloride 

11 

of  the  composition:  2LaClg. SLagOg  . 

The  chief  difficulty  with  the  method  of  Hirsch  was  the 
time  required  for  the  conversion  of  the  nitrates  to  chlorides.  The 

following  method  was  found  to  be  more  rapid  and  convenient. 

Since  the  pure  material  used  consisted  of  the  double 

magnesium  nitrates  of  lanthanum,  it  was  necessary  to  remove  the 
magnesium.  To  the  water  solution  of  the  nitrates  was  added  a 
sufficient  amount  of  NH^Cl  to  prevent  the  precipit at ion  of  Mg(OH)g. 
It  was  determined  that  sufficient  NH^Cl  should  be  added  until  the 
amount  was  equal  to  appr oxirnately  one-half  the  theoretical  amount 
of  NH^OH  needed  to  insure  complete  precipitation.  It  was  found 
necessary  to  repeat  the  precipitation  6 times,  adding  the  required 
amount  of  NH^Ol  each  time  and  washing  the  precipitate  by  decanta- 
tion several  times  with  water.  The  filtrate  from  the  last  precipi- 
tation showed  a trace  of  magnesium  upon  the  addition  of  UagHPOq. 
However,  a small  portion  of  the  precipitate  was  dissolved  in  HC1 

and  a large  excess  of  NH^Cl  and  NH^OH  added  to  precipitate  the  lan- 
thanum. Magnesium  was  3hown  to  be  absent  when  N agHPO 4 was  added 
to  the  filtrate.  In  separating  magnesium  from  lanthanum  in  this 
way,  an  appreciable  amount  of  lanthanum  material  is  lost.  mis  is 
probably  due  to  the  reversible  reaction  which  has  been  discussed 
above  under  the  method  of  Prandtl  and  Rauch enberger . Other  workers 


. 


. 


' 

. 


. 


. 

. 

1 m 


i 


7 


in  this  laboratory  have  since  found  that  magnesium  and  lanthanum 
may  be  completely  separated  with  two  precipitations  of  the  rare 
earth  oxalate  in  dilute  nitric  acid  solution  with  a minimum  less 
of  lanthanum  material. 

The  balk  of  the  material  was  then  dissolved  in  dilute 
HC1  and  evaporated  down  as  far  as  possible  cn  the  steam  bath.  Heat- 
ing was  continued  with  a ga.s  flame  until  a small  amount  of  the 
material  which  was  removed  and  placed  on  a marble  slab  solidified 
to  a moderately  hard  mas 3.  The  rest  of  the  material  was  then  pour- 
ed out  and  allowed  to  cool.  The  marble  slab  was  previously  par- 
affined by  dissolving  paraffine  in  ether  and  pouring  the  solution 
over  the  marble.  At  first,  paraffine  was  simply  rubbed  on,  but 
difficulty  was  experienced  in  the  sticking  of  the  solidified  mater- 
ial to  the  slab.  It  3eems  that  the  solution  containing  the  par- 
affine penetrates  the  pore3  in  the  marble,  preventing  sticking.  No 
basic  chloride  was  formed,  although  it  was  found  if  the  heating 
were  carried  too  far,  this  difficulty  would  arise.  The  mass  was 
then  ground  as  finely  as  possible  and  placed  in  a drying  oven  at 

?G°-8C°  for  several  days.  Under  no  circumstances  was  it  possible 

0 

to  raise  the  temperature  above  80  ^without  the  basic  salt  being 
formed.  It  was  thought  that  if  dried  air  were  circulated  above 
the  material,  more  rapid  drying  could  be  obtained.  However,  basic 
chloride  was  formed  in  all  cases  and  the  conclusion  was  reached 
that  it  is  impossible  to  raise  the  temperature  above  80°C  in  the 
presence  of  air  without  basic  salt  being  formed. 

The  chlorides  were  then  further  dried  in  an  atmosphere 
of  dry  HC1  gas.  The  waste  ga3  was  passed  into  a bottle  in  which  a 


. 


. 


. 


. 


. 


* 

i 


- 8 - 

small  jet  cf  water  was  constantly  being  sprayed.  The  excess 
water  after  dissolving  the  HC1  passed  out  of  the  bottom  of  the 
bottle.  The  chlorides  were  heated  in  the  following  manner.  Two 
electric  furnaces  18"  long,  8"  outside  diameter,  si"  inside 
diameter,  which  were  constructed  by  Dr.  H.  C.  Xremers,  were  placed 
in  series.  A pyrex  glass  tube  3"  in  diameter  was  placed  in  and 
through  the  furnaces  sc  that  about  8"  of  the  tube  extended  from 
one  end  of  each  of  the  furnaces.  When  the  first  runs  were  carried 
out,  the  chloride  was  placed  directly  in  the  tube  and  the  furnaces 
connected  in  3erie3  with  the  electric  current.  In  drying  the 
material  by  raising  the  temperature  gradually,  several  tubes  broke 
for  some  unknown  reason.  The  material  was  then  placed  in  a smaller 
tube  of  lj"  in  diameter  and  this  tube  and  contents  placed  inside 
the  larger  tube.  No  further  difficulty  was  experienced  with 
broken  tubes.  In  order  to  save  time,  the  furnaces  were  kept  at 
different  temperatures  oy  connecting  them  to  different  sources  of 
electric  current.  It  was  found  that  if  the  material  were  kept  at 
a temperature  of  125°-150c  for  7-3  hours,  the  temperature  could  be 
raised  rapidly  to  3CCc  without  basic  chloride  being  formed.  Con- 
sequently, the  furnaces  were  kept  a.t  these  two  temperatures.  The 
tube  containing  the  material  was  placed  in  the  cooler  furnace  for 
the  required  length  of  time  and  then  pushed  forward  into  the  hotter 
furnace  where  the  dehydration  was  completed  in  2 or  3 hours.  In 
this  connection  it  might  be  mentioned  that  a final  temperature  of 
at  least  3C0°C  was  found  to  be  necessary  to  drive  off  all  traces 
of  water.  If  a small  amount  of  basic  chloride  were  present  before 
the  material  was  placed  in  the  furnace,  the  HC1  gas  reconverted  it 


* 


. 


. 

■ . 


- 


. 


/ 


- 9 - 


to  the  normal  chloride. 

After  each  electrolytic  ru.n,  the  undecomposed  material 
was  recovered.  The  melt  was  dissolved  in  dilute  KC1  and  filtered. 
Oxalic  acid  was  added  to  the  acid  solution  and  the  lanthanum  oxa- 
late precipitate  washed  several  times  by  decantation.  The  oxalate 
was  calcined  in  an  electric  muffle  at  about  ?OC°C,  and  the  oxide 
dissolved  in  dilute  HC1.  The  anhydrous  chloride  was  again  ob- 
tained as  described  above. 


. 


. 


. 

. 


. 


■ 


- 10  - 


FACTORS  IN  ELECTROLYSIS 

There  are  numerous  factors  which  enter  into  the 
electrolysis  of  the  fused  anhydrous  chlorides  and  upon  which  the 
quantity  of  metal  produced  is  dependent. 

The  Cell 

The  first  in  importance  is  concerned  with  the  cell, 

the  material  composing  it,  the  size,  and  shape. 

6 

Mathmann  used  a copper  cell  hut  this  type  was  not 

considered  because  of  the  difficulty  in  constructing  it.  The 

choice  of  material  was  limited  by  the  fact  that  the  rare  earth- 

metals  alloy  more  or  les3  easily  with  other  metals.  In  the  case 

of  carbon  or  graphite,  carbides  are  formed  and  in  the  case  of 

iron,  alloys  of  iron  are  formed.  Since  the  corrosion  of  a graphite 

cell  is  stated  to  be  less  than  if;  of  the  corrosion  of  a carbon  cell 

12 

graphite  was  used  instead  of  carbon  . 

The  cell  should  be  sufficiently  large  so  as  to  be  un- 
affected by  slight  changes  in  external  conditions  but  small  enough 
to  conserve  material.  The  most  suitable  size  which  met  these  re- 
quirements wa,s  found  to  be  a cell  whose  inside  diameter  was  about 
2 inches  and  about  4-5  inches  in  height. 

A cylindrical  shaped  cell  is  more  efficient  than  a 
square  shaped  cell  because  of  the  more  uniform  heating.  Best  re- 
sults are  obtained  when  the  inside  of  the  cell  tapers  to  the 
bottom.  In  this  way,  the  bottom  tends  to  become  hotter  than  it 
otherwise  would,  which  is  very  necessary  in  order  tc  obtain  a 


regulus  of  metal 


r 


. 

■■ 

. 

: 


. ....  .7.  . 


- 11  - 


Electrodes 

The  electrodes  come  next  into  consideration.  The 
cell  itself  may  act  as  the  cathode  or  an  insulated  cathode  may 
project  upward  through  the  cell.  The  cathode  should  be  sufficient- 
ly small  so  that  a large  quantity  of  heat  i3  produced  within  a 
small  area,  as  a cell  of  this  design  is  used  with  that  end  in  view. 

The  anode  may  be  composed  of  either  carbon  or  graphite. 
Carbon  is  probably  the  least  desirable  of  the  two  materials  be- 
cause the  greater  resistance  produces  excessive  heating.  Further- 

13 

more,  car  con  is  more  easily  attacked  by  the  chlorine  , thereby 
introducing  carbon  into  the  bath.  For  these  reasons,  graphite' 
anodes  were  used  in  the  later  experiments. 

The  anode  should  be  sufficiently  large  so  as  to  obtain 
a reasonable  current  density.  However,  the  anode  should  not  be  3C 
large  that  electrolysis  takes  place  between  the  walls  of  the  cell 
and  the  anode  rather  than  from  the  bottom  of  the  cell  and  the 
anode.  Also,  the  larger  the  anode,  the  greater  the  current  density 
required  to  supply  sufficient  heat  to  keep  the  bath  molten.  In 
addition,  chlorine  i3  more  easily  evolved  with  a smaller  anode. 
However,  the  use  of  a very  small  anode  i3  limited  by  the  fact  that 
excessive  heating  of  the  anode  takes  place,  thereby  aiding  the  re- 
action between  the  liberated  metal  and  the  anode  forming  a carbide. 
The  ratio  of  the  diameter  of  the  cell  to  the  diameter  of  the  anode 
as  4 is  to  1-2  was  found  the  most  suitable. 

Composition  of  Electrolyte 

In  the  choice  of  materials  to  compose  the  electrolyte. 


- 12  - 

the  melting  point  and  specific  gravity  of  various  mixtures  should 
he  taken  into  consideration  as  well  as  the  probable  reaction  of 
the  melt  on  the  metal.  The  specific  gravity  of  the  mixture  of 
fused  salts  was  approximately  3,  while  that  of  the  metal  i3  3.15, 
The  difference  between  the  two  specific  gravities  is  sufficient  to 
allow  the  liberated  metal  to  fall  to  the  bottom  of  the  cell.  The 
melting  point  of  lanthanum  i3  claimed  to  be  810°  w while  that  is 
the  melt  was  about  300°. 

Sodium  chloride  was  used  to  the  extent  of  about  15 $ 

of  the  total  amount  of  rare  earth  chloride  added.  The  conductivity 

13 

is  relatively  high,  thereby  raising  the  temperature  of  the  bath  . 
Even  though  there  is  a possibility  of  double  chlorides  of  sodium 
and  lanthanum  being  formed,  sodium  chloride  is  used  because  it  in- 
creases the  current  efficiency  by  reducing  metal  fog  formation  and 
vaporization  of  the  lanthanum  chloride  and  metal.  However,  when 
used  in  large  amounts,  sodium  chloride  actually  reduces  the  effi- 
ciency. 

Oettel  found  in  the  electrolysis  of  magnesium  chloride, 

14 

that  powder  formation  was  obviated  by  the  use  of  calcium  fluoride  . 
His  explanation  was  that  the  surface  tension  effect  and  the  dis- 
solving of  traces  of  oxide  from  the  surface  of  the  globules  aided 

the  powdered  metal  to  coalesce.  The  solubility  of  metallic  alum- 

15 

inum  in  the  melt  is  increased  by  the  addition  of  sodium  fluoride 
and  because  the  same  effect  probably  occurs  to  a less  or  greater 
extent  in  the  electrolysis  of  lanthanum  chloride,  the  amount  of 
potassium  fluoride  added  should  be  as  am all  as  possible. 


. 


. 


. 


- J 

. 

. 


. 


- 13  - 


Radi  at  ion 

Several  runs  "became  viscous  shortly  after  starting 
the  electrolysis  due  to  excessive  radiation  even  though  the  cell 
was  imbedded  in  silocel.  Consequently,  in  the  later  runs  an 
external  heating  element  was  used  to  obtain  a finer  control  of 
the  temperature. 

Temperature 

For  economical  production,  the  temperature  in  the 
neighborhood  of  the  cathode  3hould  just  exceed  the  melting  point 
of  the  metal  and  the  rest  of  the  electrolyte  should  be  as  much  as 
possible  below  this  temperature  but  above  the  point  of  fusion  of 
the  electrolyte.  Faraday’s  law  is  valid  for  the  electrolysis  of 
fused  salts  -and  hence  the  current  efficiency  may  be  calculated 
from  the  ampere  hours  and  quantity  of  metal  formed.  Causes  which 
lower  the  current  efficiency  are  far  more  active  at  higher  temper- 
atures than  at  lower  temperatures.  In  the  electrolysis  of  fused 
lead  chloride  and  also  fused  caustic  soda,  no  metal  is  obtained  if 
the  temperature  is  high  Furthermore,  a low  temperature  allows 
a solid  layer  of  salt  to  form  on  the  walls  of  the  cell,  protecting 
the  cell  from  corrosion. 


Amperage 

The  amperage  should  be  sufficiently  high  to  supply 
heat  to  the  melt  bat  at  the  same  time  should  be  low  enough  to 
prevent  metal  fog  formation.  Between  30  and  50  amperes  were  used 
in  the  mo3t  successful  runs. 


. 


' 

♦ 

. 


. 


- 14  - 


Decomposition  Voltage 

The  decomposition  voltage  depends  upon  the  nature  of 
the  electrolyte,  the  nature  of  the  electrodes,  and  the  temperature. 
The  voltage  necessary  for  decomposition  diminishes  as  the  tempera- 
ture rises,  due  to  the  greater  tendency  of  LaClj  to  dissociate. 

From  the  point  of  view  of  voltage  alone,  it  would  be  advisable  to 
use  a high  voltage  out  this  is  more  than  neutralized  by  increased 
wear  and  tear  of  the  apparatus  and  by  the  heat  expenditure  necessary 
to  compensate  for  radiation  losses.  At  the  same  time,  the  current 
efficiency  is  decreased. 


*:  • ' ' 


’ ' 


' • 


. 


< 


- 15- 

ELECTROLYSIS  OF  THE  FUSED  CHLORIDES 
The  chief  difficulties  involved  in  the  electrolysis 

were : 

A.  The  bath  ’'freezing"  or  becoming  thick,  thereby  producing 
metallic  conduction  of  the  bath; 

B.  Formation  of  carbide; 

C.  Presence  of  "anode  effect"  which  lowers  the  currect  effi- 
ciency; 

D.  Loss  of  metal  in  other  ways  than  the  formation  of  carbide. 
All  of  the  above  difficulties  were  studied  in  the  hope  of  finding 
the  cause 3 and  the  proper  remedies. 

A.  Excessive  radiation  caused  the  bath  to  "freeze" 

very  easily.  This  could  not  be  obviated  even  by  well  insulating 

the  cell  with  silocel.  It  was  not  deemed  advisable  to  use  a larger 

anode  for  the  reasons  stated  under  a discussion  of  the  electrodes. 

Consequently,  heating  elements  were  made  to  fit  each  cell.  The 

elements  were  constructed  according  to  directions  given  by  Dr.  H. 

1 7 

C.  Kremers  and  proved  very  suitable. 

Unless  potassium  fluoride  is  present,  the  addition  of 
a large  amount  of  basic  chloride  tends  to  make  the  bath  viscous, 
thus  preventing  the  easy  evolution  of  chlorine  gas.  However,  the 
normal  anhydrous  chloride  was  readily  obtained,  and  ths  chloride 
added  to  the  bath  contained  little,  if  any,  basic  chloride. 

The  formation  of  a higher  melting  salt  such  a3  the 
oxide  or  carbide  necessitates  a higher  temperature  in  order  to 
keep  the  bath  molten.  The  oxide  is  dissolved  by  the  potassium 


-15- 

fluoride  "out  the  carbide  is  not  3c  easily  removed.  In  the  runs 
where  the  hath  became  viscous  because  of  the  formation  of  carbide, 
the  electrolysis  had  to  be  stopped. 

A small  amount  of  barium  chloride  increased  the  resis- 
tance of  the  bath  and  kept  the  electrolyte  well  fused. 

The  conductivity  of  fused  salts  increases  considerably 
with  rise  of  temperature.  Hence,  the  conductivity  of  the  melt  may 
be  increased  by  temporarily  raising  the  temperature  of  the  external 
unit  and  then  allowing  the  Joule  heating  effect  to  maintain  the 
temperature. 

B.  The  formation  of  carbide  was  aided  materially  by  the 

deterioration  of  the  graphite  anode  due  to  a high  current  density. 

o 15 

Aluminum  and  carbon  form  the  carbide  at  1000  C 
Hence,  it  is  reasonable  to  suppose  that  a high  temperature  favors 
the  formation  of  lanthanum  carbide. 

A large  quantity  of  carbide  was  formed  when  a graphite 
cell  was  U3ed.  It  was  found  impossible  to  prevent  the  formation 
of  carbide  with  such  a cell  and  in  the  later  runs,  an  iron  cell 
was  used. 

C.  "Anode  effect",  that  is,  sparking  at  the  anode,  is 
undesirable  because  it  results  in  a low  current  efficiency  and  a 
disintegration  of  the  anode.  It  is  probably  due  to  the  electrode 
becoming  covered  with  a film  cf  chlorine  gas  through  which  the 
current  can  only  pass  as  an  arc.  This  film  may  be  removed  by  stir- 
ring or  raising  the  anode  from  the  melt  for  a moment.  The  removal 
may  also  be  accomplished  by  reversing  the  current  for  a moment  or 


« 


. 


- 17 


by  increasing  the  temperature  at  constant  current  density,  or  in 
other  words,  by  increasing  the  current  through  the  external  heat- 
ing unit. 

A high  current  density  causes  rapid  electrolysis 
attended  by  the  evolution  of  a large  amount  of  chlorine.  The 
"anode  effect"  was  more  noticeable  at  the  beginning  of  the  elec- 
trolysis when  a copious  evolution  of  gas  was  taking  place.  It  is 
estimated  that  the  anode  effect  is  likely  to  occur  when  the  current 

O 

density  exceeds  4-5  amps./cmf  in  the  case  of  hard  carbon  and  7-8 
3 IS 

amps./c ml  in  the  case  of  graphite  J . Since  NaCl  has  a smaller 
conductance  than  LaCl^,  the  current  density  ma3r  be  lowered  by  the 
addition  of  NaCl,  thereby  preventing  the  "anode  effect". 

If  the  voltage  exceeded  8-10  volts  the  "anode  effect" 
made  its  appearance.  In  all  of  the  runs,  the  voltage  seldom  ex- 
ceeded 7 volt 3. 

D.  Even  after  the  metal  is  formed,  it  may  become  dis- 
sipated in  several  ways. 

Volatilization  may  occur  if  the  temperature  is  too 

high  and  the  proper  procedure  in  this  case  is  to  lower  the  voltage. 

Metal  fog  or  the  distribution  of  finely  powdered  metal 

throughout  the  melt  is  a source  of  considerable  annoyance.  In  the 

case  of  the  electrolysis  of  caustic  soda,  the  yield  of  metal  at  a 

temperature  above  535°  was  practically  zero  due  to  the  increased 

19 

diffu3ivity  of  the  metal  in  the  electrolyte'".  Metal  in  a finely 
divided  state  is  produced  also  by  a high  current  density.  The 
addition  of  a neutral  salt  such  as  NaCl  prevents,  largely,  metal 
fog  formation.  It  wa3  found  advisable  to  raise  the  temperature 


- 18  - 

of  the  cell  near  the  end  of  the  ran'  by  raising;  the  temperature  of 
the  heating  element  and  by  ’’shorting”  the  cell  every  few  minutes. 

At  the  same  time  the  temperature  was  raised,  the  melt  was  stirred 
with  a tungsten  rod  so  as  to  coagulate  the  finel3r  disseminated 
metal.  The  use  of  potassium  fluoride  in  obtaining  a regulus  of 
metal  has  been  stated  above. 

Oxidation  of  the  metal  by  the  air  may  form  another 
source  of  loss.  This  difficulty  may  be  remedied  by  keeping  the 
cell  partially  covered  during  electrolysis. 

The  metal  may  react  with  the  melt  forming  sub-salts 
and  other  compounds.  If  perfectly  anhydrous  LaClg  is  not  used, 
the  introduction  cf  water  causes  a rapid  reaction  to  take  place 
according  to  the  equation: 

SLa+SHgO  - 3La(0Hh-h3H2. 

When  a graphite  cell  was  used,  a considerable  amount 
of  metal  united  with  the  cell  forming  a carbide;  in  fact,  some 
runs  produced  carbide  only  and  no  metal.  In  the  case  cf  an  iron 
cell,  there  is  a tendency  for  FeClg  to  form.  The  current  efficiency 
is  lowered  because  of  the  alternate  reduction  and  oxidation  of  the 
FeClg  at  the  cathode  and  anode  respectively.  In  fact,  it  is  stated 
that  less  than  0.1$  FeClg  reduces  the  current  efficiency  more  than 
30^?°  The  formation  cf  FaClg  i3  largely  prevented  by  allowing  a 
solid  layer  cf  salt  to  form  on  the  inside  of  the  cell. 

The  metal  may  react  with  the  chlorine  which  is  liber- 
ated at  the  anode.  Allowing  the  chlorine  to  escape  rapidly  by 
frequent  stirring  inhibits  this  reaction. 


. 


- 


. 

. 

. 


. 

. 


. 


. 

■ 

. 

. 


- 19 


EXPEEIMEN TAL  RE  SUL TS 

In  the  first  few  experiments,  the  cerium  group  chlor- 
ides were  used  to  work  out  a general  procedure  without  running  the 
risk  of  losing  lanthanum  material,  a3  these  salts  are  more  easily 
prepared  than  lanthanum  salts.  The  anhydrous  chlorides  were  pre- 
pared in  the  same  way  as  the  anhydrous  lanthanum  chloride.  In 
cases  where  the  finely  divided  metal  was  obtained,  it  was  found 
that  the  metal  was  in  a very  impure  form.  Attempts  to  fuse  it 
under  UaCl  resulted  in  the  oxide.  Other  attempts  were  made  to 
obtain  it  in  a pure  state  so  that  it  might  be  pressed  into  a rod 
and  the  particles  sintered  together  as  in  the  case  of  tungsten. 

The  powder  was  mixed  with  anhydrous  bromofcrm  in  hopes  that  the 
bromoform  which  has  a specific  gravity  between  that  of  the  metal 
and  carbon  would  effect  a separation,  but  this  method  failed  as 
the  particles  of  carbon  held  too  tenaciously  to  the  metal.  This 
explains  the  effort  made  to  obtain  the  metal  in  a pure  coherent 
mass.  In  all  the  runs,  graphite  anodes  were  used  of  various  size3. 

1.  A graphite  crucible  was  used,  the  average  diameter 

/ 

being  Sn.  The  diameter  of  the  anode  in  this  case  was  5/6”.  The 
electrolyte  was  composed  of  ITaCl,  KF,  and  cerium  chloride.  A 
regulus  of  metal  weighing  5 grains  was  obtained,  together  with  a 
large  amount  cf  carbide  and  finely  divided  metal.  The  melt  was 
dissolved  from  the  crucible  with  cold  water,  the  water  decomposing 
the  carbide  and  having  little  effect  on  the  metal.  Hydrogen  wa3 
evolved  upon  the  addition  of  acid  to  the  powder  and  the  residue 
consisted  mainly  of  powdered  graphite.  The  current  was  7 volts 


. 

, 

* 


1 . 


. 


- 30  - 

and  20  amperes  for  3i  hours . The  temperature  of  the  bath  was  a 
cherry  red  and  an  auxiliary  heating  element  maintained  this  temper- 
ature. 

3.  An  attempt  was  made  to  duplicate  this  run  by  re- 
producing the  same  conditions;  however,  it  resulted  in  finely 
divided  metal  being  formed  and  also  metallic  sodium,  which  upon 
rising  to  the  surface  burned  with  a yellow  flame,  sometimes  with 
explosive  violence.  It  was  found  that  upon  lowering  the  voltage, 
the  formation  of  sodium  and  the  "anode  effect"  ceased, 

3.  Because  of  the  difficulty  in  maintaining  a suffi- 
ciently high  temperature  in  the  previous  rim,  a -J"  anode  was  used 
in  this  case.  Instead  of  KF,  KOI  was  used  as  it  was  thought  that 
the  lowered  specific  gravity  of  the  bath  and  the  lowered  tempera- 
ture (sp.  gr.  KC1  = 1.984;  KF  = 2.481;  — rn.p.  KC1  * 773°;  KF  = 
830°)  would  result  in  the  aivided  metal  settling  rapidly  to  the 
bottom  of  the  cell  and  forming  a coherent  mass.  However,  the  re- 
sults obtained  were  similar  to  those  of  the  previous  run. 

-4.  In  this  run  an  anode  of  diameter  was  used  ’’cut 
only  powdered  metal  and  carbide  were  obtained.  The  voltage  and 
the  amperage  were  the  same  a3  in  the  preceding  experiments,  but 
the  electrolysis  had  to  be  stopped  at  the  end  of  2i  hours  because 
of  the  "freezing"  cf  the  bath. 

5.  It  was  thought  that  the  formation  of  carbide  might 
be  obviated  by  coating  the  inside  of  the  cell  to  within  about 
of  the  bottom  with  alundum  cement.  The  anode  was  in  diameter, 
the  voltage  14  and  the  amperage  10,  A very  small  amount  cf  KF  was 
used  in  this  case  and  consequently  after  the  run,  the  alundum 


. 


' •'  • 


- 


r.  ■ ■ . 

w1  • • v/  y 


. 


. 


; 


' 


*’ 


■ 


. 


; 

- 31  - 

cement  lining  was  found  to  be  fairly  intact.  LaClj  was  used  in- 
stead of  C3CI3  and  carbide  and  no  coherent  metal  were  obtained. 

8,  At  this  point  it  was  decided  to  abandon  the  idea  of 
carrying  on  the  electrolysis  in  a graphite  cell  because  of  the 
formation  of  large  amounts  of  carbide.  It  was  decided  to  use  a 
soft  steel  crucible,  4"  in  depth  and  3”  in  diameter.  The  cell 
formed  the  cathode  and  the  anode  was  a 7/8”  graphite  rod.  In  order 
to  obtain  a higher  temperature,  0,  greater  conductance  was  needed 
and  so  only  the  chlorides  and  oxides  of  cerium  were  added.  It  was • 

1 thought  that  the  oxide  would  oxidize  any  free  carbon  present  in  the 
bath.  The  voltage  was  7 and  the  amperage  300.  At  the  end  of  3 
hours,  the  electrolysis  was  stopped  as  the  high  current  density 
produced  a hole  in  the  crucible  allowing  the  melt  to  flow  out  into 
the  external  heating  unit. 

7.  A new  type  of  cell  wa3  then  devised.  A 4”  length 

of  a 3"  pipe  with  a -J”  reduced  coupling  screwed  into  the  end  formed 
the  cell.  A tungsten  rod  of  3/8”  diameter  projected  upward  for  a 
distance  of  about  1”  through  the  bottom  of  the  cell  and  was  well 
insulated  with  asbestos  string.  The  rod  projected  outside  of  the 
bottom  of  the  cell  for  about  3”  and  in  order  to  protect  it  from 
oxidation  was  brazed  with  copper.  Chloride  and  oxide  of  lanthanum 
were  used  and  an  amperage  of  between  100-150  was  obtained  at  8 
volt 3,  Very  little  carbide  was  formed  and  the  metal  obtained  was 
in  a finely  divided  state.  In  this  run,  an  external  heating  ele- 
ment was  not  used  because  the  high  conductivity  cf  the  bath  kept 
the  temperature  sufficiently  high. 

8.  Since  the  metal  fog  formation  was  evidently  due  to 


. 

- 33  - 

the  high  temperature  3nd  high  current  density,  and  in  order  to  re- 
duce vaporization  of  the  chloride,  it  was  decided  to  U3Q  an  elec- 
trolyte consisting  of  NaCl,  KF  and  LaClg.  No  external  heat  was 
applied  and  difficulty  was  experienced  in  keeping  the  hath  molten. 

It  was  necessary  to  "short"  the  cell  frequently  30  as  to  keep  the 
bath  fluid.  This  run  gave  the  first  indication  of  success  and  aboul 
3 grams  of  coherent  metal  were  obtained  lying  close  to  the  cathode 
and  showing  that  the  high  temperature  of  the  cathode  was  necessary 
to  melt  and  coagulate  the  metal.  30-50  amperes  and  7-3  volts  were  1 
used. 

9.  In  order  to  be  more  conserving  of  material,  a 
smaller  cell  whose  diameter  was  1-J”  was  constructed  similar  to  the 
cell  used  in  the  previous  experiment.  A heating  element  was  made 
to  fit  this  cell.  Because  of  the  success  obtained,  this  run  will 
be  described  in  some  detail.  A 5/8 " anode  was  U3ed  and  the  elec- 
trolyte consisted  of:  150  3.  LaClj,  30  g,  KF,  and  35  g,  NaCl,  A 
small  amount  of  NaCl  and  KF  was  melted  by  "shorting"  the  cell  with 
a i"  short  carbon  rod.  When  the  temperature  was  sufficiently  high 
to  keep  the  bath  molten,  the  plug  was  removed  and  the  electrolysis 
begun.  The  electrolysis  was  carried  on  for  4 hours  at  ? volts  and 
30-40  amperes.  During  the  last  \ hour  of  electrolysis  the  temper- 
ature was  raised  by  adding  BaCl^  in  small  amounts  and  raising  the 
voltage.  The  melt  was  stirred  from  time  to  time  with  a tungsten 
rod.  12.3  grams  of  metal  in  coherent  globules  were  obtained,  the 
largest  globule  weighing  3.2  grams.  This  weight  of  metal  repre- 
sented a current  efficiency  of  about  6 per  cent,  Upon  analysis, 

0.77  per  cent  of  iron  was  found  to  be  present  and  not  a trace  of 
tungsten.  


- 33  - 

10.  It  was  than  decided  to  carry  out  an  electrolysis 
in  an  iron  cell.  The  cell  was  identical  to  that  containing  the 
insulated  tungsten  cathode  except  for  the  fact  that  the  iron  cell 
in  this  case  was  the  cathode.  The  anode  was  5/8”  and  the  elec- 
trolyte was  composed  of  LaCl^,  KF  and  NaCl  as  before.  Thirty 
amperes  at  5 volts  were  used.  The  electrolysis  was  carried  on  for 
4 hours  and  9.1  grams  of  metal  in  coherent  particles  were  obtained, 
the  largest  particle  weighing  3 grams.  The  metal  showed  about  15$ 
iron  upon  analysis. 

11.  Because  of  the  contamination  of  the  metal  with  iron 
when  an  iron  cell  was  used,  it  was  decided  to  attempt  the  use  of  a 
graphite  cell  again.  The  cell  was  identical  to  that  used  in  the 
first  run  'out  this  run  yielded  better  results.  21.4  grams  of  metal 
in  coherent  particles  were  obtained,  the  largest  particle  weighing 
6.3  grams.  This  represented  a current  efficiency  of  10  per  cent. 
The  electrolyte  wa3  composed  of  335  grams  of  LaCl^,  50  grams  of 

KF  and  40  grams  of  NaCl.  The  metal  thus  obtained  is  in  a high 
state  of  purity  although  the  efficiency  cannot  be  made  to  equal  the 
efficiency  which  could  be  obtained  with  an  iron  cell,  due  to  the 
formation  of  carbide. 

12.  In  hopes  of  raising  the  current  efficiency, 
another  run  was  made  using  the  same  graphite  cell  and  a 3/4” 
anode.  The  electrolyte  consisted  of  335  grams  LaCl^  30  grams 
KF,  and  30  grams  NaCl.  This  run  was  very  successful  and  resulted 
in  the  obtaining  of  68 .4  grams  oi  metal,  most  of  tne  metal  .cin~ 
in  three  large  pieces  and  the  largest  particle  weighing  33  grams* 
The  electrolysis  was  carried  on  for  3 hours  at  50  amperes  and  7-8 


— 3«3a— 

volts.  The  amperage  represented  a lowering  of  about  30  amperes 
from  that  of  the  previous  run.  At  the  end  of  the  run,  the  tempera- 

j 

ture  of  the  melt  was  raised  by  "shorting"  the  cell  for  intervals 
of  a minute  or  two.  Very  little  carbide  was  formed  and  the  current 
efficiency  was  37.2  percent.  The  increase  in  efficiency  over  the  | 
previous  run  was  probaoly  due  to  the  use  of  smaller  amounts  of  KF 
and  NaCl  and  the  lowered  current  density. 


. 


. 


. 


- 34  - 

SUMMARY . 

1,  The  new  method  of  Prandtl  and  Rauchenberger  in  the 
separation  of  lanthanum  from  neodymium  and  praseodymium  was  tried 
with  encouraging  results, 

2,  A 3tudy  was  made  of  the  various  methods  of  obtain- 
ing anhydrous  LaCl^  and  the  dehydration  of  the  partially  dried 
LaClg  in  a pyrex  glass  tube  in  a current  of  dry  HOI  gas  met  ’with 
success, 

3,  An  exhaustive  study  was  made  of  the  electrolysis 
of  fused  anhydrous  LaOl^  and  it  was  found  that: 

A.  Electrolysis  in  an  iron  cell  containing  an  insulated 
tungsten  cathode  produced  metal  of  a fair  degree  of  purity; 

B.  Then  an  iron  cell  acting  as  a cathode  wa3  used,  metal  con- 
taminated with  iron  resulted; 

C.  Metal  in  a high  state  of  purity  may  be  obtained  by  elec- 
trolysis in  a graphite  cell. 


, 

. 


, 


. 

. 


. 


25 


BIBLIOGRAPHY 

1.  J.  F.  Spencer,  The?  Metals  of  the  Rare  Earths,  (1919). 

2.  Mo Sander,  Pogg.  Ann.,  46 . 64S  (1339);  i old. , 47.  207,  (1839); 

Corapt.  rend.,  3,  358-57,  (1839). 

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